1. Field of the Invention
The present invention relates to an internal combustion engine and more particularly to an internal combustion engine having balancing means. More specifically, the present invention pertains to bearing means of the balancer shaft for such internal combustion engine.
2. Description of the Prior Art
In reciprocating piston engines, vibrations are produced due to the mass of reciprocating parts. In order to eliminate such vibrations, proposals have been made to provide balancer shafts carrying balancing weights and rotate the balancer shafts to thereby counterbalance the vibrations. For example, Japanese patent application No. 49-119778 filed on Oct. 16, 1974 and published for public inspection on Apr. 21, 1976 under the disclosure No. 51-46607, there is disclosed an engine having a pair of balancer shafts arranged to extend in parallel with the engine crankshaft at the opposite sides of the cylinder block. The balancer shafts are driven through a timing belt by the crankshaft in directions opposite to each other. In the structure disclosed by the Japanese patent application, a substantial amount of balancing torque must be produced so that the balancer shafts must be supported by sufficiently rigid bearing structure. The Japanese patent application teaches to provide such bearing structure at side portions of the cylinder block. However, this solution is not preferable because the cylinder block becomes bulky and complicated in configuration.
Japanese utility model application No. 57-137605 filed on Sept. 13, 1982 and disclosed for public inspection on Mar. 19, 1984 under the disclosure No. 59-42334 discloses an engine wherein a balancer shaft in driven through a gear mechanism by the engine crankshaft. In this engine too, the crankcase is sidewardly expanded to provide a space for arranging the balancer shaft.